In general, a perceived quality of a data communications service depends, in part, on the speed of the service. Such speed may be impacted by impedance mismatches between a transmission line and a customer premises equipment (CPE) device, such as a modem. For example, problems between a central office and a customer premises (i.e., outside plant problems) may reduce data communication speeds. Additionally, the speed of the data communications service may be impaired by elements within the customer premises, such as poor wiring, faulty equipment, etc. Hence, there is a need for a system and method to determine an impedance mismatch.